1. Field of the Invention
The present invention relates to methods and systems for controlling ammonia slip, and in particular, for controlling ammonia slip downstream of a selective catalyst reduction (SCR) system.
2. Description of Related Art
Powerplant and engine exhaust systems can include an SCR reactor for removing nitrogen oxides (NOx) from exhaust gases. A reductant, such as ammonia, is injected into the exhaust gas stream entering the SCR reactor to remove NOx from the exhaust gas. A problem associated with SCR reactors is “ammonia slip,” i.e., unreacted ammonia passing through the SCR reactor and exiting the exhaust system with the exhaust gas. It would be desirable to accurately control parameters of the exhaust system, such as the amount of ammonia injected into the exhaust stream, to minimize ammonia slip.